linux-kernel - Re: [PATCH] memory-hotplug: use PFN_DOWN in should_add_memory

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Message-ID: <20151118165134.GB19150@dhcp22.suse.cz>
Date:	Wed, 18 Nov 2015 17:51:34 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Geliang Tang <geliangtang@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Gu Zheng <guz.fnst@...fujitsu.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Tang Chen <tangchen@...fujitsu.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	David Vrabel <david.vrabel@...rix.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memory-hotplug: use PFN_DOWN in should_add_memory_movable

On Wed 18-11-15 21:31:32, Geliang Tang wrote:
> Use PFN_DOWN() in should_add_memory_movable() to keep the consistency
> of this file.

I really detest this patch and c8e861a531b0 ("mm/memory_hotplug.c: use
PFN_DOWN()") which has started to use PFN_DOWN in that file likewise.
It obfuscates a perfectly understandable construct of addr->pfn
conversion by a macro which I have to really check what it does because
the name suggests I am rounding an existing pfn down.

This really doesn't help the readability.

> 
> Signed-off-by: Geliang Tang <geliangtang@....com>
> ---
>  mm/memory_hotplug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 67d488a..7c44ff7 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1205,7 +1205,7 @@ static int check_hotplug_memory_range(u64 start, u64 size)
>   */
>  static int should_add_memory_movable(int nid, u64 start, u64 size)
>  {
> -	unsigned long start_pfn = start >> PAGE_SHIFT;
> +	unsigned long start_pfn = PFN_DOWN(start);
>  	pg_data_t *pgdat = NODE_DATA(nid);
>  	struct zone *movable_zone = pgdat->node_zones + ZONE_MOVABLE;
>  
> -- 
> 2.5.0
> 
> 
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-- 
Michal Hocko
SUSE Labs
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